1. Field of the Invention
The present invention relates to a control method/system for controlling downshifting in an at least partially automated mechanical transmission system. In particular, the present invention relates to the control of downshifting in a vehicular automated mechanical transmission system wherein the system, to prevent "hunting," after an upshift, decreases the engine speed at which a downshift will be requested until the passage of a period of time and/or the occurrence of a predetermined event, such as engine speed exceeding a predetermined reference value.
More particularly, the present invention relates to control logic which will sense high load operating conditions occurring after an upshift to reset the downshift points to the normal values thereof from the anti-hunt values.
2. Description of the Prior Art
Fully or partially automated mechanical transmission systems for vehicular use are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,648,290; 4,722,248; 4,850,236; 5,389,053; 5,487,004; 5,435,212 and 5,755,639.
Controls for automated mechanical transmission systems, especially wherein shifting is accomplished while maintaining the master clutch engaged, wherein single and/or skip shift feasibility is evaluated are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,576,065; 4,916,979; 5,335,566; 5,425,689; 5,272,939; 5,479,345; 5,533,946; 5,582,069; 5,620,392; 5,489,247; 5,490,063 and 5,509,867, the disclosures of which are incorporated herein by reference.
Anti-hunt logic for automatic mechanical transmissions is known in the prior art. See U.S. Pat. Nos. 4,361,060 and 4,698,763, the disclosures of which are incorporated herein by reference.
As may be seen by reference to aforementioned U.S. Pat. Nos. 4,361,060 and 4,698,763, to avoid undesirably rapid downshifts after an upshift, or undesirably rapid upshifts after a downshift (i.e., "hunting"), it is known to adjust or modify the shift points or shift profiles after a shift by increasing the upshift engine speed after a downshift and/or decreasing the downshift engine speed after an upshift. It is also known that the shift points or profiles should be reset to their normal positions to achieve desired vehicle operation as quickly as possible after the likelihood of hunting has been minimized. Typically, the shift profiles are reset in two increments, one related to the passage of time and the other to engine speed "passing through" a reset engine speed (i.e., going from greater than to less than, or going from less than to greater than, the reset engine speed).
While the above-referenced automatic transmission control systems are very effective to control an automatic transmission by selecting a desired gear ratio which will tend to optimize the fuel economy and/or performance of the vehicle in view of the sensed parameters and then to command a shift into the selected gear ratio, such control systems were not totally satisfactory. In particular, such control systems were not totally satisfactory, as the portion of reset of the downshift shift profiles to the normal positions thereof from a last shift upshift offset related to engine speed was not highly responsive to high throttle position (.gtoreq.90%) coupled with a lack of vehicle acceleration (d/dt(OS).ltoreq.0). These are conditions indicative of an upshift occurring just as a vehicle begins to climb an upgrade.